[GHC] #12468: GADTs don't refine hole types

[GHC]

#12468: GADTs don't refine hole types
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        Reporter:  benjamin.hodgson  |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  MacOS X           |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 > However, I do think it would still be helpful to have some indicator in
 the error message of the fact that the context gives us an equality. After
 all, such information can be very useful when you're trying to fill in a
 hole.  Something along the lines of:

 Yes, that's plausible and do-able; along the lines of displaying the
 "relevant bindings".  Does anyone want to have a go?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12468#comment:3>
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